Telephone switching centers generally include switching networks which comprise a number of input and output terminals and a number of crosspoints. The individual crosspoints are selectively controlled to complete communication paths between the input and output terminals of the network. Historically, network crosspoints have comprised metallic contacts which provide a very linear, low resistance communication path. With advances in semiconductor technology, semiconductor devices are being used in place of the metallic crosspoints. The use of such semiconductor devices tends to increase the speed of network operation and to reduce the size. Typical semiconductor crosspoints, however, exhibit higher resistance and increased nonlinearity when compared to their metallic predecessors. This is particularly true for semiconductor crosspoints such as thyristors and gated diode switches which are used in networks capable of handling large voltages and/or currents.
When relatively low voltage signals are applied to a network comprising crosspoints having nonlinear conduction characteristics, severe distortion of such signals can take place. This occurs primarily because such crosspoints are generally at their most nonlinear at voltages near zero. Such distortion becomes a particular problem when low voltage tests are being applied through a semiconductor network, since any distortion of the signals can greatly change test results. Additionally, when a circuit such as a telephone subscriber loop is being tested, no modifications can be made to the loop circuit in an attempt to linearize the network without also distorting the test results. An arrangement in accordance with the present invention permits the transmission and reception of low level signals through a switching network comprising nonlinear semiconductor crosspoints with little or no distortion of such signals.